The present invention relates to a method for automatically determining coefficients for correcting the deflection of a stylus in a digitizing device and automatically correcting a displacement of the stylus using the correction coefficients thus obtained.
In a digitizing device, digitized data which defines a three-dimensional model is generally determined from the path of the center of the stylus which is obtained by adding an output from a position detector for detecting the relative positions of a three-dimensional model and a tracer head and the output from the tracer head for measuring the amount of the displacement of the stylus. Accordingly, it is necessary to use a stylus having a diameter as small as is practically possible in order to obtain digitized data which are faithful to the form of the three-dimensional (3-D) model.
The stylus is held at the tracer head by means of a spring, and exhibits a displacement which is proportional to the contact pressure between the stylus and the three-dimensional model. For example, as shown in FIG. 1, the stylus ST is displaced by a displacement EX in response to the contact pressure F between the stylus ST and the three-dimensional model BK, as expressed by the following equation (1): EQU F=k.sub.1 .multidot.EX (1)
wherein k.sub.1 is an elastic coefficient of a spring.
However, when the stylus ST having a small diameter such as shown in FIG. 2 is used to obtain digitized data which is as faithful as possible to the three-dimensional model configuration, the stylus ST sometimes deflects by the contact pressure F between it and the three-dimensional model BK because of the low rigidity of the stylus ST. The deflection amount TX in the stylus ST is proportional to the contact pressure F (refer to an equation (2) below): EQU F=k.sub.2 .multidot.TK (2)
wherein k.sub.2 denotes an elastic coefficient of the stylus ST.
As a result, the precision of the digitized data becomes deteriorated since the deflection amount TX is added as an error to the normal displacement EX. In the prior art, the deflection amount of a small-diameter stylus is therefore determined on the basis of a large-diameter stylus in which the deflection is negligible, and the inputted displacement is corrected accordingly to achieve higher precision of the digitized data. However, this necessitates a precise determination of the deflection amount for each stylus used, thereby inconveniently requiring a relatively large amount of time expended.